The present invention relates to an automated assembly station for mechanical parts and a management method therefor.
Automated precision assembly stations comprising a structure bearing a plurality of locking inserts for mutual positioning of the parts to be assembled are well known in the prior art. Assembly devices, for example articulate robot arms, permanently fasten together the parts positioned by the inserts and the finished product is then drawn from the station.
Assembly can take place by welding, gluing, riveting, clinching et cetera depending on specific requirements. Examples of assembly stations are the welding stations on assembly lines for motor vehicles or their parts.
Usually when the assembly line of which the station is a part is made operational there is performed a fine calibration of the position of the inserts which represent ideally key reference points of the structure it is desired to assemble, that is to say points through which the structure must pass to be defined optimal. For this purpose the inserts are shaped with gripping surfaces (usually consisting of a fixed part and a facing complementary movable part) which represent the ideal configuration at those points of the object to be assembled. The surfaces of the inserts are generally shaped starting from the mathematics of the surface of the part it is desired to secure and taken from the CAD drawings representing it.
Various factors concur however to make less than ideal the configuration of the real object produced which will be subject to geometrical errors causing its deviation from the optimal configuration. Degradation factors can be proper to the assembly technique used or due to geometrical changes which intervene after initial calibration of the station. For example in the case of welding assembly variations or drifting of the welding parameters such as those due to consumption of the electrode, variation of the electrical current or welding time, change of position in the sequence of performance of the welding points et cetera can intervene. Similar factors can be traced for the other assembly methods also.
Geometrical variations can be caused for example by maintenance operations and/or adjustments to the station, wear of movable parts or even variations in the physical parameters of the parts assembled such as in the composition, thickness, shape et cetera of the parts to be assembled. Typical are the changes in thickness of pressed sheet metal parts with changes in the production lot.
For each reference point there is thus defined a tolerance range within which the object produced must fall to be accepted at least as a satisfactory part.
Usually purposive measurement stations arranged at line end perform sample measurements of the parts produced and if necessary emit an unacceptability signal which warns of the need to reject the parts in production and seek along the line the reason or reasons which produced the undesired change. The difficulty of identifying the responsible station among the plurality present in the line is apparent.
In addition, as the measurement is done on a sampling basis a certain number of defective parts are produced before the defect is signaled.
Since sequential assembly operations are generally performed on various stations before obtaining the final part which is measured on a sampling basis errors produced in an early station and which if discovered early would be correctable or limitable become irreparable and also involve members assembled in the subsequent stations.
All this results in wasted time, money and materials. The general purpose of the present invention is to overcome the above shortcomings by supplying an innovative assembly station and a management method allowing timely and accurate discovery of unacceptable deviations from the ideal form. Another purpose of the present invention is to point out in a timely manner changes in the reference geometry of the station resulting for example from faulty maintenance or wear. In addition another purpose is to facilitate recalibration of the station reference members after maintenance operations and/or worn parts replacement.